The present invention relates to liquid condition sensing apparatus for sensing a liquid condition such as a liquid level, and more specifically to capacitive liquid condition sensing apparatus.
A published Japanese patent application publication No. 63-79016 discloses a capacitive liquid level sensor for sensing a liquid level of gasoline or oil used in a motor vehicle. This sensor is arranged to be submerged at least partly in the liquid and to sense the level of the liquid. This liquid level sensor includes a reference electrode pair submerged invariably under the liquid, a measuring electrode pair to be submerged partly in the liquid, and a sensing circuit to measure the liquid level by using a ratio between a capacitance between the reference electrodes and a capacitance between the measuring electrodes.
By employing the reference electrodes in addition to the measuring electrode, this liquid level sensor can measure the liquid level accurately despite variation in the dielectric constant of the liquid.